[Test-Equipment] Frequency Measuring Test

[Mike Feher]

Hi Guys -

I do not believe that propagation delays will cause frequency measurement
errors. Unless we are talking about something like doppler. Plain delay
should have no effect. It will however have an effect on any time related
information sent along at the same time. I have a Cesium, about a dozen
rubidiums, and a pair of GPS disciplined double oven crystal types. I really
also do not fully appreciate the advantage of a GPS disciplined Rubidium
over a GPS disciplined crystal in a double oven. We all know that for real
short term stability a crystal is hard to beat. Rubidiums become better in
the long term and Cesiums ever better yet. But in the short term, within the
loop bandwidth, they all have crystals, so not much difference. In the long
term, the GPS takes over. As pointed out, the biggest problem would be to
somehow lock on to the actual signal to be measured and then compared. I
really wonder if the ARRL has the equipment necessary to determine their
transmitted frequency to these accuracies, or if they are going to
coordinate with NIST or some equivalent. Additionally, at these accuracies
only a statistical measurement, like an Allen Variance, or even a simple
average, would be of use, as there would be too much fluctuation in the
comparison device. I'll have to dig out my last issue of QST to see what
they have in mind. Thanks & 73 - Mike



Mike B. Feher, N4FS
89 Arnold Blvd.
Howell NJ, 07731
(732) 901-9193


----- Original Message -----
From: "Dave Emery" <die@die.com>
To: "Glenn Little" <glittle@awod.com>
Cc: "Gary Chatters" <gc@radix.net>; <test-equipment@mailman.qth.net>
Sent: Tuesday, September 24, 2002 1:40 AM
Subject: Re: [Test-Equipment] Frequency Measuring Test


> On Tue, Sep 24, 2002 at 12:13:43AM -0400, Glenn Little wrote:
> > I wonder if they have the ability to measure their reference frequency
as
> > well as some in the field. There are a number of people with GPS
disiplined
> > Rubidium standards. Unless you have a Hydrogen MASER, they are hard to
beat.
>
> So the real issue for those with modern technology frequency
> standards is actually not the raw time base accuracy but figuring out
> how to make a reliable measurement of the unknown signal with anything
> like the accuracy of their house standard.
>
> Certainly a HF signal received by skywave is only easily measured
> to maybe one part in 10^7 or 10^8 due to propagation effects which is
> a long long way away from a couple of parts in 10^11 that a GPS
disciplined
> rubidium standard will do routinely.   I suppose figuring out an algorithm
> to filter out the propagation induced errors might be interesting, but
> certainly something very different from the frequency measuring tests
> of past years, which stressed skills at calibrating and setting up
> hardware and using it skillfully.
>
> I could - and I suppose many many others with fully synthesized
> HF rigs referenced to a 10 mhz input from a rubidium GPS disciplined
> standard could too -  measure a HF signal by just tuning it in with a
> known BFO offset and processing the resulting audio with a soundcard to
> make a best estimate of the frequency of the beat note minus propagation
> related shifts.  And if I really was anal, I could hack the soundcard to
> derive its sample clock from a synthesizer driven off the 10 mhz
> rubidium standard too (eg replace the crystal osc used for timing with a
> clock input from a synthesizer or even just a DDS NCO chip driven from
> the rubidium).
>
> I suppose a local VHF or UHF signal might be measurable with
> much greater accuracy, but then one gets into multipath and all sorts of
> other  effects and of course the test signal only reaches a few people.
>
>
>
> >
> > 73
> > Glenn
> > WB4UIV
> >
> > At 11:35 PM 9/23/02 -0400, Gary Chatters wrote:
> > >The latest issue of QST announced that ARRL is bringing
> > >back the frequency measuring test.  Anyone here thinking of
> > >participating?
> > >
> > >Gary
>
> --
> Dave Emery N1PRE,  die@die.com  DIE Consulting, Weston, Mass.
> PGP fingerprint = 2047/4D7B08D1 DE 6E E1 CC 1F 1D 96 E2  5D 27 BD B0 24 88
C3 18
>
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